Preparation method and application of fluorine-aluminum-doped sulfate catalyst

Abstract

The present invention discloses a preparation method and application of a fluorine-aluminum-doped sulfate catalyst, the preparation method comprising the following steps: A1. sulfate, aluminum salt and fluoropolymer are dissolved in a solvent, and at 55-85° C., stirred to form a gel, wherein the mass ratio of the sulfate, aluminum salt and fluoropolymer is 1:(0.2-1.9):(0.2-1.9); A2. the gel is dried and calcined to obtain a fluorine-aluminum-doped sulfate catalyst, wherein the fluorine-aluminum-doped sulfate catalyst is a sulfate-alumina-aluminum fluoride composite catalyst. When the fluorine-aluminum-doped sulfate catalyst of the present invention is used for the fluorine-chlorine exchange reaction of trifluoromethane and trichloromethane, the acidic position of the catalyst that is conducive to the main reaction can be accurately regulated, and the disproportionation side reaction of R22 and R21 can be effectively suppressed. The CHF3 conversion rate can reach 30%, and the catalytic activity is high. At the same time, the introduction of fluorine gives the catalyst good resistance to fluorine loss and improves catalyst stability.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and in particular to a preparation method of a fluorine-aluminum-doped sulfate catalyst and application thereof in a fluorine-chlorine exchange reaction. Background Art

[0002] Trifluoromethane (CHF3, HFC-23) is an inevitable byproduct of the industrial production of difluorochloromethane (CHClF2, HFC-22). Its greenhouse gas potential is approximately 14,800 times that of carbon dioxide, making it the second-highest greenhouse gas. Currently, high-temperature incineration (above 1200°C) is the primary method of industrial disposal, but this process is costly and wastes resources. Therefore, resource conversion of trifluoromethane is of great significance.

[0003] Patent CN112979410A discloses a fluorine-chlorine exchange reaction between HFC-23 and halogenated hydrocarbons under the catalytic action of a main catalyst and a metal oxide. The main catalyst is a chromium, aluminum, or magnesium-based catalyst or a catalyst in which chromium, aluminum, or magnesium is supported on activated carbon / graphite. The metal oxide is selected from at least one metal oxide of K, Na, Fe, Co, Cu, Ni, Zn, or Ti. The HFC-23 conversion rate is between 24.7% and 26.7%, which is lower than 30%.

[0004] Patent CN112973685A discloses a method for reducing catalyst carbon deposition in the resource utilization of HFC-23. The resource utilization is achieved by carrying out a fluorine-chlorine exchange reaction between HFC-23 and a halogenated hydrocarbon. The catalyst of the fluorine-chlorine exchange reaction includes a main catalyst and a precious metal. The precious metal is selected from at least one of Pt, Pd, Ru, Au or Rh, and the addition amount is 0.01 to 2 wt%. The CHF3 conversion rate is between 26.7 and 27.1%, which is lower than 30%.

[0005] Patent EP2172441A discloses a method for fluorinating chloroalkanes or fluorochloroalkanes. The method primarily involves the vapor-phase fluorination of chloroalkanes or fluorochloroalkanes using HFC-23 as a fluorinating agent, such as the fluorination of CHCl3 to produce HCFC-22. The catalyst can be fluorides, oxyfluorides, or mixtures of Mg, Al, Zn, or Cr. For example, using AlF3 as a catalyst, under reaction conditions of 240°C, a CHF3 / CHCl3 ratio of 1.17, and a residence time of 30.9 seconds, the HFC-23 conversion can reach 38%, with selectivities of 4-8% for both HCFC-22 and HCFC-21. Using strongly acidic Lewis acid catalysts such as AlF3, the reported CHF3 conversion is generally high, but the product selectivity is low, and no catalyst stability results are disclosed.

[0006] Patent CN103467239A develops a process for preparing HCFC-22 by cracking HFC-23, comprising mixing the raw materials HFC-23 and methane chloride in a molar ratio of 0.1 to 10 and feeding them into a reactor filled with a catalyst, using a catalyst such as magnesium, aluminum, zinc, or chromium fluoride supported by gamma alumina, fluorinated gamma alumina, or activated carbon, and feeding HFC-23 and CHCl3 in a molar ratio of 1:1 into a 250°C nickel tube reactor with a residence time of 35 seconds. After sampling one hour after feeding, the molar contents of HFC-23, CHCl3, HCFC-22, and HCFC-21 are 28.2%, 28.3%, 20.7%, and 20.6%, respectively. The trifluoromethane conversion rate can reach more than 40%, and the HCFC-22 content can be more than 20%. However, the catalyst stability results are also not disclosed.

[0007] For strongly acidic Lewis acid catalysts such as AlF3, the CHF3 conversion rate is high, but because it is easy to be deactivated by carbon deposition, the stability is generally poor, and it is difficult to take into account both good activity and stability at the same time. Sulfate is a new type of solid acid material. In addition to being a catalyst, it can also be used as a catalyst carrier in a variety of reaction systems such as fluorine-chlorine exchange, dehydrofluorination and hydrodechlorination, and is receiving more and more attention. However, due to the low acidity of sulfate, the general raw material conversion rate is low. Fluorine doping makes aluminum sulfate less likely to be destroyed by HF in this system and becomes more stable. Fluorine-doped sulfate can be obtained by calcining the fluorine-doped sulfate, regulating the acidity of the catalyst while having good stability. Its special Lewis acid sites also determine that it will have good application prospects in the field of fluorine chemical industry. Summary of the Invention

[0008] In order to solve the above technical problems that strong Lewis acid catalysts such as AlF3 have high activity but are prone to carbon deposition and deactivation, and sulfate catalysts have good stability but poor activity, the present invention proposes a preparation method of a fluorine-aluminum-doped sulfate catalyst. When the fluorine-aluminum-doped sulfate catalyst is used for a fluorine-chlorine exchange reaction, on the one hand, sulfate-aluminum oxide-aluminum fluoride produces a synergistic catalytic effect. At the same time, the HF generated by the decomposition of the fluorine-containing polymer of the aluminum oxide is partially fluorinated to form aluminum fluoride. By adjusting the content distribution of aluminum oxide and aluminum fluoride, the acidic position of the catalyst that is conducive to the main reaction can be accurately controlled, and the disproportionation side reaction of R22 and R21 can be effectively suppressed, thereby promoting the main reaction, and increasing the CHF3 conversion rate by more than 30%, and the catalyst maintains good stability.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A method for preparing a fluorine-aluminum-doped sulfate catalyst, comprising the following steps:

[0011] A1. A sulfate, an aluminum salt, and a fluoropolymer are dissolved in a solvent and stirred at 55 to 85° C. to form a gel; the mass ratio of the sulfate, the aluminum salt, and the fluoropolymer is 1:(0.2 to 1.9):(0.2 to 1.9);

[0012] A2. The gel is dried and calcined to obtain a fluorine-aluminum-doped sulfate catalyst, wherein the fluorine-aluminum-doped sulfate catalyst is a sulfate-alumina-aluminum fluoride composite catalyst.

[0013] In step A1:

[0014] The sulfate is selected from at least one of chromium sulfate, magnesium sulfate, aluminum sulfate, iron sulfate, barium sulfate or nickel sulfate, preferably chromium sulfate and / or aluminum sulfate.

[0015] The aluminum salt is selected from at least one of aluminum nitrate, aluminum carbonate, and aluminum isopropoxide, and is preferably aluminum nitrate.

[0016] The fluorine-containing polymer is at least one selected from polyvinyl fluoride, polyvinylidene fluoride, polyethylene-chlorotrifluoroethylene copolymer, polyethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, preferably polyvinyl fluoride and / or polyvinylidene fluoride.

[0017] The solvent is selected from at least one of isopropyl alcohol, propylene glycol, tetrahydrofuran, dimethyl sulfoxide or dimethylformamide, preferably isopropyl alcohol.

[0018] The mass ratio of the sulfate, aluminum salt, and fluoropolymer is 1:(0.2-1.9):(0.2-1.9), preferably 1:(0.3-1.8):(0.3-1.8). At this mass ratio, the prepared fluorine-containing aluminum-doped sulfate catalyst has suitable acidity and specific surface area, can effectively inhibit the disproportionation reaction of R22 and R21, and improve the activity of the main reaction.

[0019] In step A2:

[0020] The drying temperature of the gel is 80-180° C., preferably 100-160° C., and the drying is carried out in an oven.

[0021] The gel is calcined at a heating rate of 2-6°C / min, a temperature of 290-460°C, a time of 4-16h, and an atmosphere of at least one of air, oxygen, and nitrogen. The calcination is carried out in a muffle furnace.

[0022] The inventors have found through research that the sulfate-alumina-aluminum fluoride composite catalyst prepared above is particularly suitable for fluorine-chlorine exchange reactions, especially for the reaction of preparing difluorochloromethane and monofluorodichloromethane by fluorine-chlorine exchange between trifluoromethane and chloroform.

[0023] Therefore, the present invention also provides a method for resource utilization of trifluoromethane, which comprises: using trifluoromethane and chloroform as raw materials, and preparing difluorochloromethane and monofluorodichloromethane through a fluorine-chlorine exchange reaction under the action of a sulfate-alumina-aluminum fluoride composite catalyst prepared by any of the above preparation methods.

[0024] The molar ratio of trifluoromethane to chloroform is 1:1.5 to 1:4.5, the reaction temperature is 290 to 410°C, and the reaction pressure is 0.10 to 0.60 MPa. Preferably, the molar ratio of trifluoromethane to chloroform is 1:2 to 1:4, the reaction temperature is 300 to 400°C, and the reaction pressure is 0.20 to 0.40 MPa.

[0025] Research has found that in the fluorine-chlorine exchange reaction of trifluoromethane and trichloromethane, the products R22 and R21 are prone to disproportionation side reactions. The specific reaction formula is as follows:

[0026] R22 disproportionation: 3CHClF2→2CHF3+CHCl3

[0027] R22 disproportionation: 2CHClF2→CHF3+CHFCl2

[0028] R21 disproportionation: 2CHCl2F → CHCl3 + CHClF2

[0029] During the reaction, CHF3 and CHCl3 fluorine-chlorine exchange main reaction and the disproportionation side reaction of R22 and R21 are all carried out on Lewis acid sites, and there is a competitive relationship between the main and side reactions. The strong acid position is more conducive to the progress of the disproportionation side reaction, resulting in a reduction in the main reaction CHF3 conversion rate. The catalyst of the present invention is modified by the addition of aluminum salt and doping with fluoropolymer. During the roasting process, the aluminum salt is converted into aluminum oxide, and the fluoropolymer is connected to make aluminum oxide be incorporated into sulfate. At the same time, the fluoropolymer gradually decomposes and releases HF, forming a fluoride ion active center on the surface of the sulfate and aluminum oxide composite catalyst, and partially fluorinated to generate aluminum fluoride. By regulating the aluminum salt and fluoropolymer mass ratio and preparation conditions, the mass distribution of aluminum oxide and aluminum fluoride can be controlled in a direction. Aluminum oxide acidity is weaker, and aluminum fluoride acidity is stronger. By regulating the mass distribution of the two, combined with the synergistic effect of sulfate, the acidity of the catalyst can be accurately regulated. When the mass distribution of aluminum oxide and aluminum fluoride is 30-50% and 50-70% of the total mass of aluminum oxide and aluminum fluoride, respectively, the catalyst has an acid strength and acidity suitable for the main reaction, which is conducive to the main reaction. The CHF3 conversion rate can reach over 30%, and the above-mentioned disproportionation side reaction of R22 and R21 can be suppressed, thereby promoting the fluorine-chlorine exchange reaction between trifluoromethane and trichloromethane. At the same time, the release of hydrogen fluoride during the calcination process causes the catalyst to gradually form a porous material, becoming loose, increasing the specific surface area of ​​the catalyst, and further facilitating the main reaction.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention regulates the raw material dosage ratio and preparation conditions so that the catalyst has an acid strength and acidity suitable for the fluorine-chlorine exchange reaction of trifluoromethane and trichloromethane, can inhibit the disproportionation side reaction of R22 and R21, promote the main reaction, improve the reaction activity, and make the CHF3 conversion rate reach more than 30%.

[0032] 2. The fluorine-aluminum-doped sulfate catalyst of the present invention has a loose structure and a large specific surface area. At the same time, the introduction of fluorine gives the catalyst good resistance to fluorine loss, allowing the catalyst to maintain good activity and stability. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0034] Example 1

[0035] This example provides the preparation of a fluorine-aluminum-doped sulfate catalyst, and the specific steps are as follows:

[0036] 40g of chromium sulfate and 60g of aluminum nitrate were dissolved in a mixed solution of 50mL of isopropanol, 40g of polyvinyl fluoride (PVF) was added, and the mixture was stirred in an 85°C water bath until it formed a gel. The mixture was then foamed and dried at 140°C for 4 hours to remove the organic solvent. The gel was then placed in a muffle furnace and heated to 390°C at a heating rate of 3°C / min and held there for 14 hours. The mixture was then cooled to room temperature to obtain a chromium sulfate-alumina-aluminum fluoride composite catalyst, in which the mass distributions of alumina and aluminum fluoride were 43% and 57% of the total mass, respectively, designated as Cat 1. The resulting catalyst was pressed into tablets at 18MPa and crushed to 10-20 mesh size for later use.

[0037] Example 2

[0038] The operation of this embodiment is the same as that of Example 1, except that aluminum carbonate is used instead of aluminum nitrate as the aluminum salt, and the amount used remains unchanged to prepare a chromium sulfate-aluminum oxide-aluminum fluoride composite catalyst, in which the mass distributions of aluminum oxide and aluminum fluoride are 41% and 59% of the total mass of the two, respectively, and is recorded as Cat2.

[0039] Example 3

[0040] The operation of this embodiment is the same as that of Example 1, except that aluminum isopropoxide is used instead of aluminum nitrate as the aluminum salt, and the amount used remains unchanged to prepare a chromium sulfate-aluminum oxide-aluminum fluoride composite catalyst, in which the mass distributions of aluminum oxide and aluminum fluoride are 38% and 62% of the total mass of the two, respectively, and is recorded as Cat3.

[0041] Example 4

[0042] The operation of this embodiment is the same as that of Example 1, except that the amount of aluminum nitrate used is changed from 60 g to 40 g, and a chromium sulfate-aluminum oxide-aluminum fluoride composite catalyst is prepared, in which the mass distribution of aluminum oxide and aluminum fluoride is 31% and 69% of the total mass of the two, respectively, and is recorded as Cat4.

[0043] Example 5

[0044] The operation of this embodiment is the same as that of Example 1, except that the amount of aluminum nitrate used is changed from 60 g to 72 g, and a chromium sulfate-aluminum oxide-aluminum fluoride composite catalyst is prepared, in which the mass distribution of aluminum oxide and aluminum fluoride is 47% and 53% of the total mass of the two, respectively, and is recorded as Cat5.

[0045] Example 6

[0046] The operation of this embodiment is the same as that of Example 1, except that the amount of polyvinyl fluoride is changed from 40 g to 32 g, and a chromium sulfate-aluminum oxide-aluminum fluoride composite catalyst is prepared, in which the mass distribution of aluminum oxide and aluminum fluoride is 48% and 52% of the total mass of the two, respectively, and is recorded as Cat6.

[0047] Example 7

[0048] The operation of this embodiment is the same as that of Example 1, except that the amount of polyvinyl fluoride is changed from 40 g to 72 g, and a chromium sulfate-aluminum oxide-aluminum fluoride composite catalyst is prepared, in which the mass distribution of aluminum oxide and aluminum fluoride is 32% and 68% of the total mass of the two, respectively, and is recorded as Cat7.

[0049] Example 8

[0050] The operation of this embodiment is the same as that of Example 1, except that polyvinylidene fluoride (PVDF) is used instead of polyvinyl fluoride as the fluoropolymer, and the amount used remains unchanged to prepare a chromium sulfate-aluminum oxide-aluminum fluoride composite catalyst, in which the mass distribution of aluminum oxide and aluminum fluoride is 40% and 60% of the total mass of the two, respectively, and is recorded as Cat 8.

[0051] Example 9

[0052] The operation of this embodiment is the same as that of Example 1, except that aluminum sulfate is used instead of chromium sulfate in the same amount as the sulfate, to prepare an aluminum sulfate-aluminum oxide-aluminum fluoride composite catalyst, in which the mass distributions of aluminum oxide and aluminum fluoride are 42% and 58% of the total mass of the two, respectively, and is recorded as Cat 9.

[0053] Comparative Example 1

[0054] The operation of this example is the same as that of Example 1, except that no fluorine-containing polymer is used, and an aluminum-doped chromium sulfate catalyst is prepared, in which aluminum exists only in the form of aluminum oxide and does not contain aluminum fluoride, and is recorded as Cat B1.

[0055] Comparative Example 2

[0056] The operation of this embodiment is the same as that of Example 1, except that the amount of polyvinyl fluoride is changed from 40 g to 100 g, and a chromium sulfate-aluminum oxide-aluminum fluoride composite catalyst is prepared, in which the mass distribution of aluminum oxide and aluminum fluoride is 22% and 78% of the total mass of the two, respectively, and is recorded as CatB2.

[0057] Comparative Example 3

[0058] The operation of this example is the same as that of Example 1, except that no aluminum salt is used, and a fluorine-containing chromium sulfate catalyst is prepared without aluminum oxide and aluminum fluoride, which is denoted as Cat B3.

[0059] Comparative Example 4

[0060] The operation of this embodiment is the same as that of Example 1, except that the amount of aluminum nitrate is changed from 60 g to 100 g, and a chromium sulfate-aluminum oxide-aluminum fluoride composite catalyst is prepared, in which the mass distribution of aluminum oxide and aluminum fluoride is 55% and 45% of the total mass of the two, respectively, and is recorded as CatB4.

[0061] Comparative Example 5

[0062] The operation of this example is the same as that of Example 1, except that sulfate is not used, and a fluorine-containing aluminum oxide catalyst is prepared, in which the mass distribution of aluminum oxide and aluminum fluoride is 42% and 58% of the total mass, respectively, and is recorded as Cat B5.

[0063] Comparative Example 6

[0064] The operation of this embodiment is the same as that of Example 1, except that calcium sulfate is used instead of chromium sulfate in the same amount as the sulfate, to prepare a calcium sulfate-alumina-aluminum fluoride composite catalyst, in which the mass distributions of alumina and aluminum fluoride are 38% and 62% of the total mass of the two, respectively, and is recorded as CatB6.

[0065] Example 10

[0066] This embodiment provides a method for resource utilization of trifluoromethane, comprising:

[0067] Using CHF3 and CHCl3 as raw materials, a fluorine-chlorine exchange reaction is carried out under the action of Cat1~Cat9 and CatB1~B6. The specific steps are as follows:

[0068] 10mL of catalyst was loaded into a fixed-bed reactor consisting of a stainless steel tube with an inner diameter of 20mm and a length of 800mm. To accelerate catalyst evaluation efficiency, stringent reaction temperature and residence time conditions were selected: a reaction temperature of 380°C, a residence time of 3s, a pressure of 0.1MPa, and a molar ratio of trifluoromethane to trichloromethane of 1:1.8. The catalyst's aluminum oxide and aluminum fluoride contents were characterized, and the reaction products were qualitatively and quantitatively analyzed. The results are shown in Table 1 below:

[0069] Table 1 Trifluoromethane and chloroform reaction results

[0070]

[0071] As can be seen from the result of Table 1 above, under harsh reaction conditions, when the fluorine-containing aluminum-doped sulfate catalyst of the present invention is used for the fluorine-chlorine exchange reaction of trifluoromethane and trichloromethane, compared to aluminum-doped chromium sulfate catalyst (Comparative Example 1), fluorine-containing chromium sulfate catalyst (Comparative Example 3) and fluorine-containing aluminum oxide catalyst (Comparative Example 5), all have good activity and stability, and sulfate, aluminum salt, fluoropolymer mass ratio, sulfate, aluminum salt, fluoropolymer type difference also make catalyst have different performance. Fluorine-containing aluminum-doped sulfate catalyst prepared under preferred conditions, by regulating the mass distribution of aluminum oxide and aluminum fluoride, CHF3 conversion rate reaches 30%, and has good stability. Outside this scope (Comparative Example 2 and Comparative Example 4), then CHF3 conversion rate is lower than 30% or catalyst stability is poor.

Claims

1. A method for preparing a fluorine-aluminum-doped sulfate catalyst, characterized in that: The preparation method comprises the following steps: A1. A sulfate, an aluminum salt, and a fluoropolymer are dissolved in a solvent and stirred at 55 to 85° C. to form a gel; the mass ratio of the sulfate, the aluminum salt, and the fluoropolymer is 1:(0.2 to 1.9):(0.2 to 1.9); A2. The gel is dried and calcined to obtain a fluorine-aluminum-doped sulfate catalyst, wherein the fluorine-aluminum-doped sulfate catalyst is a sulfate-alumina-aluminum fluoride composite catalyst; the gel is calcined at a heating rate of 2 to 6°C / min, a calcination temperature of 290 to 460°C, a calcination time of 4 to 16 hours, and a calcination atmosphere of at least one of air, oxygen, or nitrogen.

2. The method for preparing a fluorine-aluminum-doped sulfate catalyst according to claim 1, wherein: The sulfate is selected from at least one of chromium sulfate, magnesium sulfate, aluminum sulfate, iron sulfate, barium sulfate or nickel sulfate.

3. The method for preparing a fluorine-aluminum-doped sulfate catalyst according to claim 1, wherein: The aluminum salt is selected from at least one of aluminum nitrate, aluminum carbonate, and aluminum isopropoxide.

4. The method for preparing a fluorine-aluminum-doped sulfate catalyst according to claim 1, wherein: The fluorine-containing polymer is at least one selected from polyvinyl fluoride, polyvinylidene fluoride, polyethylene-chlorotrifluoroethylene copolymer, polyethylene-tetrafluoroethylene copolymer, and polyvinylidene fluoride-hexafluoropropylene copolymer.

5. The method for preparing a fluorine-aluminum-doped sulfate catalyst according to claim 1, wherein: The solvent is selected from at least one of isopropyl alcohol, propylene glycol, tetrahydrofuran, dimethyl sulfoxide or dimethylformamide.

6. The method for preparing a fluorine-aluminum-doped sulfate catalyst according to claim 1, wherein: The mass ratio of the sulfate, the aluminum salt and the fluorine-containing polymer is 1:(0.3-1.8):(0.3-1.8).

7. The method for preparing a fluorine-aluminum-doped sulfate catalyst according to claim 1, wherein: The drying temperature of the gel is 80-180°C.

8. A method for conversion and utilization of trifluoromethane, characterized in that: Using trifluoromethane and trichloromethane as raw materials, difluorochloromethane and monofluorodichloromethane are prepared through a fluorine-chlorine exchange reaction under the action of a sulfate-alumina-aluminum fluoride composite catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. The method for conversion and utilization of trifluoromethane according to claim 8, characterized in that: In the sulfate-aluminum oxide-aluminum fluoride composite catalyst, when the mass distribution of aluminum oxide and aluminum fluoride is 30-50% and 50-70% of the total mass of the two respectively, the CHF3 conversion rate is ≥30%.

10. The method for conversion and utilization of trifluoromethane according to claim 8 or 9, characterized in that: The molar ratio of trifluoromethane to chloroform is 1:1.5 to 1:4.5, the reaction temperature is 290 to 410° C., and the reaction pressure is 0.10 to 0.60 MPa.

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